In the field of analog and mixed integrated circuits (ICs), it is known that the ICs often use, or are operably coupled to, external components.
The analog/mixed ICs are often used in safety applications. Clearly, system behaviour in safety applications must be carefully controlled, such that system operation is reliable and not jeopardised. For example, it is known that the accidental disconnection of external components, such as external filtering capacitors, may jeopardise the operation and functionality of the IC, and therefore the system.
One example is a system that utilises a voltage regulator IC, which is typically coupled to one or more external capacitors for filtering purposes. FIG. 1 illustrates a known system having a voltage regulator offering no protection, should an external capacitor be disconnected. In FIG. 1, the known system 100 comprises an analog or mixed integrated circuit 105 having an internal functional element 110. The internal functional element 110 is supplied with a voltage from voltage regulator 115; which is operably coupled to a reset circuit 120. An external filtering capacitor 130 is operably coupled between the voltage regulator 115 on the analog or mixed integrated circuit 105 and ground 135 to provide ac coupling via IC pin 125 to the voltage regulator 115.
The filtering capacitor 130 is typically of the order of μF, and hence is of a significant size. The size of the filtering capacitor 130 effectively means that it cannot be integrated on the analog or mixed integrated circuit 105, and has to be coupled to the analog or mixed integrated circuit 105 externally.
When this external capacitor 130 is disconnected, the voltage regulator 115 is still trying to regulate without the external capacitor. Hence, behaviour of the voltage regulator 115, e.g. its output voltage, is degraded; yet the voltage regulator 115 is still able to maintain enough voltage to avoid reaching a reset threshold of the reset circuit 120. The consequence is that a degraded system is running without any detection of the disconnection or, indeed, any safe, predictable state of the voltage regulator, say following a reset operation. Consequently, internal system functions, circuits or elements supplied by the voltage regulator 115 may also exhibit non-predictable behaviour, which is undesirable.
A common way to solve this problem is to introduce redundancy into the system. FIG. 2 illustrates a known system 200 having a voltage regulator 215 and employing a redundant capacitor protection arrangement for a case where an external capacitor may be disconnected.
In FIG. 2, the known system 200 comprises an analog or mixed integrated circuit 205 having an internal functional element 210. The internal functional element 210 is supplied with a voltage from voltage regulator 215, which is operably coupled to a reset circuit 220. A first external filtering capacitor 230 is operably coupled between the voltage regulator 215 on the analog or mixed integrated circuit 205 and ground 245, via pin 225, to provide ac coupling via IC pin 225 (not shown in FIG. 2) to the voltage regulator 215.
In order to provide protection to the system, a second external filtering capacitor 240 is operably coupled in parallel to the first external filtering capacitor 230 between the voltage regulator 215 on the analog or mixed integrated circuit 205 and ground 245, via pin 235. In this manner, the system employs redundancy in coupling two external capacitors to two de-coupling pins.
If either of the first or second external filtering capacitors is inadvertently disconnected, the system is still protected with the remaining connected external capacitor. In this case, the voltage regulator 215 continues to work normally. The remaining capacitor stabilizes the voltage regulator 215 and filters any noise. Each capacitor value is calculated so that the system behaviour and performance is acceptable in normal operation and if the other capacitor is disconnected for whatever reason.
However, this solution leads to an IC package with a higher pin count, component count and increased size due to an additional extra component, than is actually needed by the system, and is therefore inefficient and unnecessarily costly.
Thus, a need exists for an improved protection mechanism for a voltage regulator and associated integrated circuit system, in case of disconnection of a coupled-to external component, such as a filtering capacitor.